This invention relates to circuitry for processing color television signals. More particularly, it is concerned with apparatus for detecting color video signals from chrominance signals in color television receivers.
In color television receivers the chrominance signals are separated from the composite video signal as by appropriate filter arrangements. However, some high frequency luminance components pass through the bandpass filter separating out the chrominance signal. These unwanted components which are referred to as cross-color effects cause distortion in the colors of the display on the screen.
In order to reduce the cross-color effects so-called comb filters may be employed in addition to the usual color signal processing circuitry. Comb filters may be employed in both the luminance and the chrominance channels. The operations of these filters make use of the fact that in accordance with standard NTSC broadcast standards much of the luminance information is represented by signal frequencies concentrated about integral multiples of the horizontal line scanning frequency while the chrominance information is concentrated around frequencies which lie halfway between integral multiples of the line scanning frequency. Although the use of comb filters is an effective technique for eliminating cross-color distortion they are in addition to the circuitry required for processing and demodulating the chrominance and luminance signals, and thus add to the cost of color television receivers.